1. Field of the Invention
The present invention relates to a fuel vapor collecting device for use in a motor vehicle.
2. Description of the Related Art
A fuel vapor collecting device is used to prevent a fuel vapor rom escaping into the outside air. To this end, in a known fuel vapor collecting device using an activated carbon, fuel vapor generated from a fuel system such as a fuel tank is adsorped and temporarily retained in the activated carbon, and when the engine is operating in a predetermined operating state, the fuel vapor adsorped in the activated carbon is desorped by introducing the outside air to the activated carbon, and the fuel vapor thus desorped is fed into the engine cylinders and burned therein.
The fuel vapor adsorption ability of the activated carbon becomes higher as the temperature of the activated carbon becomes lower, and the fuel vapor desorption ability of the activated carbon becomes higher as the temperature of the activated carbon becomes higher. But the adsorption of the fuel vapor by the activated carbon is an oxothermic reaction, and consequently, since the temperature of the activated carbon becomes higher as the adsorption becomes greater, a problem occurs in that the adsorption ability of the activated carbon is gradually lowered. In addition, the desorping of the fuel vapor in the activated carbon is an endothermic reaction and, therefore, since the temperature of the activated carbon becomes lower as the desorping becomes greater, another problem occurs in that the desorption ability of the activated carbon is gradually lowered.
To eliminate these problems, a known fuel vapor collecting device comprises a plurality of fins extending outward beyond the circumferential wall of the activated carbon receiving chamber from the interior of the activated carbon receiving chamber (Japanese Unexamined Patent Publication No. 55-149622). In this fuel vapor collecting device, the adsorping ability and the desorping ability of the activated carbon are improved by discharging the heat generated when the fuel vapor is adsorbed into the outside air through the fins, to suppress an increase in temperature of the activated carbon, and when the fuel vapor is desorped, introducing heat outside of the fuel vapor collecting device into the activated carbon, through the fins, to suppress the reduction in temperature of the activated carbon.
Nevertheless, when the fuel vapor collecting device is provided with a plurality of such fins, a problem occurs in that the size of the fuel vapor collecting device is increased, and in addition, the construction of the fuel vapor collecting device becomes complicated, and thus another problem occurs in that much time and labor are required for the manufacture of the fuel vapor collecting device.